The invention relates to a signalling method used in a digital radio system wherein the signals transmitted comprise data and signalling.
The invention also relates to a transmitter used in a digital radio system wherein the signals transmitted comprise data and signalling.
The DAB system (Digital Audio Broadcasting) is a novel digital radio broadcasting system. Traditionally, radio broadcasting systems have been based on analog technique. The quality of a signal transmitted by the new digital system is extremely good compared with a signal transmitted by analog technique. Signal quality remains good even under circumstances when multi-path propagation is present. In traditional analog radio transmission, the problem is multi-path propagation, wherein a signal arriving at a receiver is reflected from several different surfaces. The signal components reflected from various surfaces, e.g. high multi-storey buildings, are received in different phases in the receiver, causing disturbances. In the DAB system, multi-path propagation does not cause problems; on the contrary, multi-path propagation improves signal quality and audibility. In the DAB system a signal is divided into sub-bands, which are quantized such that the noise generated in quantizing remains low. The DAB system improves considerably the signal quality received by car radios, for example.
The transmission level used in the system is low compared with the level used in traditional systems. In a DAB radio network, all transmitters are able to send at the same frequency. The signals of different transmitters do not interfere with other signals as the different signals sum up. On the contrary, the summing up of the signals improves audibility. However, the transmitters have to be very exactly synchronized at the same frequency. In addition, the transmission band is efficiently used in the DAB system, enabling the number of radio channels to be significantly increased.
The DAB system is used for the transmission of various services. The services may be e.g. audio or data services. The services may be transmitted e.g. across a fixed PSTN network (Public Switched Telephone Network) and a radio channel to a mobile receiver, for example, in broadcast mode. For efficient transmission of various services, the DAB system has to use efficient data management and signalling methods.
A radio channel in the DAB system may be divided into capacity units of different sizes, whereby several services and their components are simultaneously transferred to a receiver by means of a signal. Momentarily, a high-capacity service reserves a large number of capacity units, which are freed when the need for service decreases. Since the DAB system has to manage numerous internal structures and a large amount of data, which together form entire services, a lot of signalling information has to be transmitted, too. Owing to the large amount of signalling information, signalling has to be transferred to a receiver in a manner allowing rapid and efficient unpacking.
The recommendation ETS 300,401 describing the DAB system discloses how signalling according to the DAB protocol is divided into small signaIling units. However, generating signalling units by the method according to the recommendation is slow. At the same time, managing the signalling has become complex and laborious. In prior art solutions, information on signalling management has been placed in a data table, whereby unpacking the signalling at the receiving end has been difficult. This has resulted in slow retrieval of the relevant data at the receiving end. This means that the subscriber to the service has not received the service ordered or desired fast enough. In addition, arranging and changing the data included in the data table has not been sufficiently efficient with known methods.
It is the object of the present invention to provide a method of managing signalling so that relevant data is found rapidly at the receiving end and that changing the data table becomes more efficient.
This is achieved with a method described in the preamble, characterized in that the signalling is placed in a signal to be transmitted on the basis of control information that is separate from the data, the control information being used for managing the signalling.
The method is further characterized in that the signalling is placed in a signal to be transmitted on the basis of the control information, and the control information is prevented from being placed in the signal to be transmitted.
The transmitter of the invention is characterized in that the transmitter comprises control means for placing the signalling in a signal to be transmitted on the basis of control information that is separate from the data, and for preventing the control information from being placed in the signal to be transmitted, the control information being used for managing the signalling.
The method of the invention provides significant advantages. In the method, a separate signalling transmission table is used in signalling transmission, information on signalling management being placed in said table. In the method, the data is sent in a data table. The use of a transmission table enables the order of the data to be changed, and the data to be arranged without any need to change the actual data table. The method facilitates and speeds up management of the data table particularly when a large data table is concerned. The transmission table may be changed dynamically and the amount of control information can be adjusted according to the signalling need. Additionally, according to the signalling need, the transmission table can be prioritized and arranged in the desired manner. The most significant advantage is gained when unpacking a data table at a subscriber terminal. In this situation the data table is unpacked more rapidly since the subscriber terminal does not have to unpack the signalling transmission table.
The preferred embodiments of the method are also disclosed in the attached dependent claims, and the preferred embodiments of the receiver of the invention are disclosed in the attached dependent claims.